Complete knee prothesis

ABSTRACT

This prothetic device for replacing the articulation of a human knee comprises two elements adapted to be inserted the one into the femur and the other into the tibia, the femoral element having a female articulation portion adapted to be engaged by the male articulation portion of the tibial element so as to retain the latter, the male portion being releasably engageable into the female portion only when the two elements are disposed substantially at right angles to each other ; the design is such that a certain locking action is obtained in the fully stretched leg position and that during the flexion movement a certain degree of lateral movement is allowed.

[ Mar. 12, 11974 COMPLETE KNEE PROTHESlIS 22 Filed: Nov. 17, 1972 21Appl.No.:307,557

[52] US. Cl 3/1, 128/92 C, 287/12, 287/87 [51] Int. Cl. A611 l/24l [58]Field of Search 3/1, 22; 128/92 C, 92 CA, 128/92 R; 287/12, 21, 87

France 128/92 C Sweden 128/92 C Primary Examiner-Richard A. GaudetAssistant Examiner-Ronald L. Frinks Attorney, Agent, or FirmKarl F.Ross; Herbert Dubno [57] ABSTRACT This prothetic device for replacingthe articulation of a human knee comprises two elements adapted to beinserted the one into the femur and the other into the tibia, thefemoral element having a female articulation portion adapted to beengaged by the male articulation portion of the tibial element so as toretain the latter, the male portion being releasably engageable into thefemale portion only when the two elements are disposed substantially atright angles to each other the design is such that a certain lockingaction is 0btained in the fully stretched leg position and that duringthe flexion movement a certain degree of lateral movement is allowed.

7 Claims, 4 Drawing Figures 1 COMPLETE KNEE PROTHESIS BACKGROUND OF THEINVENTION:

1. Field of the Invention:

This invention relates to a novel complete prosthesis of the knee or, inother words, a prosthetics device for replacing completely thearticulation of a human knee either diseased or wounded, for example asa consequence of an accident.

This device is based on the principle that movement of articulatedobjects which has the maximum amplitude and constitutes the nearestapproach to perfection, that is, a movement that can take place in alldirections, is the movement obtained by combining a solid sphere withhollow sphere the latter being rotatably fitted in the solid sphere.

2. Description of the Prior Art:

In the human skeleton this universal movement is obtained more or lesscompletely in two joints the hip articulation and the shoulderarticulation, wherein the joint surfaces in mutual contact arecom-parable 'to those of spherical segments. In prosthetics,consequently, when the problem to be solved consisted in makingartificial joints or articulations, for example of plastic or metal, arelatively simple solution was found for the hip. In fact, it was onlynecessary to obtain the mutual engagement of two spherical segments,i.e., a hollow spherical segments secured to the hip-bone, as asubstitute for the cotyle, and a solid spherical seg ment secured bymeans of a rod to the diaphysis as a substitute for the femoralapophysis.

The problem with which praticians were confronted consistedessentiallyin fastening an inert material to a living bone. At present this problemappears to be solved satisfactorily due to the use of acrylic cement(methyl methacrylate).

However, the making of prostheses for the other joints, notably in thecase of human knees, is much more complicated. From theonset, when weobserve the mode of operation of a knee, it apparently makes onlyflexure and extension movements about an axis. Therefore, the prosthesissolution seemed .rather simple only a hinge was required, i.e., a meanspermitting a movement of revolution. Thus, nearly all knee prosthesesmade up to now were based on this easy principle.

Yet, what occurs during a knee movement? If we observe the flexureextension movement of the knee, we see that from the stretched positiona small movement of revolution obviously takes place initially, whichdoes not exceed about a point, whereafter the tibia moves backwardslittle by little while rotating about a point also undergoing a backwardmovement, whereby each point taken individually has a different radiusor curvature with respect to the preceding point. If we trace the lociof the centres of rotation, we see that they form or describe a linewhich not only moves backwards and downwards. but has radii ofdecreasing lengths in the backward direction, so as to describe a spiralcurve.

The joint bony surfaces of femoral condyles describe in the fore-and-aftdirection (logarithmic) spiral paths which guide the movement. As to thetibial plates, in the fore-and-aft direction they are slightly convex(they should be concave to accommodate the anteroposterior condyliancamber therefore, they slide and pitch). But in'the transversedirection, they are concave to meet the requirements of the transverseconvexity of the femoral condyles.

From the foregoing it will be seen that this compound movement is farfrom the simple movement of revolution, i.e., a circular movement abouta point, but in addition and simultaneously with this compound movementa torsional movement takes place which is guided by the length of theinternal condyle which is greater than the length of the externalcondyle. It is this lastmentioned movement that causes the leg to loosein flexion the abduction, the valgum it had in the extended position.

Moreover, if in the fully stretched position the knee is rigid, as itbends it can make slight lateral movements and torsional movements,which can take place due to the transverse contour or configuration ofthe joint surfaces (the femoral condyles are strongly convex in thetransverse direction, especially the external one, and the tibial platesare concave transversely and rise at their intermediate portion on theperipheries of the spines of which the abutment function is of primaryimportance). This movement is a kind of rolling" movement.

To summarize the movements taking place during the flexion extension ofthe human knee, one could say that in the antero-posterior directionthere is a pitch" movement and in the transverse direction a rolling"movement. The words pitch and rolling give a clear definition of thesystem of movements performed by the knee articulation.

But what matters most is the manner in which this movement is utilizedwhen walking the important fact is that the bearing phase of the stepoccurs substantially without any flexion. When a person is walking andthe bearing phase begins, the limb engages the ground ahead, in a fullystretched position, or if not fully stretched, it assumes this positionimmediately when the plantar bearing is complete, whereafter the otherlimb bends its knee and moves forward while the bearing limb keeps itsknee stretched and oscillates about the hip. During this phase, the kneeis stiff, tensioned and the limb oscillates. When the limb underconsideration becomes posterior, the bearing engage-ment is relieved,the knee is bent to permit the lifting of the foot which is then thrownforwards, and the same cycle is resu-med. Under these conditions it maybe said that in the really dynamic phase of walking the knee is not bentand when it is bent it does not bear anymore. Therefore, the kneestrength is required only in the stretched position. To make walkingmore comfortable it is even useful that the bent knee has a certainlaxity. Now a hinge, due to its rigidity in all positions, cannotconform to these various notions.

SUMMARY OF THE INVENTION:

The improved knee prosthesis described hereinafter is designed formeeting these various imperative requirements by attempting to producevoluntary movements of the two types as explained in the foregoing.

Nature made this achievement through a complex play, thanks to theperfection potentialities governing all its constructions. Yet, a closeapproach of this complex play may be obtained through the prosthetictechnique.

By way of preliminary explanation, let us consider firstly what takesplace in a hip, while bearing in mind the mechanical system obtained byhaving a solid sphere movably housed in a hollow sphere and providedwith a rod (the femoral apophysis carried by the diaphysal line).

This femoral sphere is movable in all directions in the fixed iliacspherical segment. This system permits a 360 movement in all directionsand about all axes.

The most logical method for measuring these movements consistsapparently in expressing the data in latitudes and longitudes. In thelanguage of space mechanics, assuming that the femoral apophysisconsists of the centre thereof, and that the femur of thigh bone orlower limb is one of the radii extending from this center, it is an easymatter to measure all the movements as a functions of the latitudes andlongitudes. Thus, for instance, all of the flexion movements areexpressed in latitudes and all the lateral movements in longitudes. Theonly requirement is to take from the onset two axes of origin orreferences axes.

The novel prosthesis of the knee according to this invention is basedaccordingly on the principle of the spherical movement or ball-joint,but within accurately defined limits very extensive latitudes, beyond90, but very limited longitudes, for example These 10 will correspond tothe necessary rolling movement, the latitude reproducing the pitchmovement.

In actual practice, this novel prosthesis is obtained as follows in itsessential structure it comprises a pair of relatively small generallyhemispherical portions i.e., a movable solid spherical portion rollingin a fixed hollow spherical portion. The solid spherical member has acylindrical extension and the hollow spherical member consists of aperfect sphere, therefore greater than the male solid spherical member.To approach the pitch movement and the rolling movement, the followingsolutions are applied in the case of the pitch movement, the solidspherical member in its vertical position, as the leg is bent, slides atthe same time backwards because the cavity containing this solidspherical member is spherical and therefore greater, so that as theflexion takes place the member recedes slightly, thus simulating therolling and sliding movement (pitch). Regarding the rolling movement, itis obtained as follows in the fully stretched position, the male memberis locked in an antero-posterior cavity the shape of which constitutesan important factor and may be defined as being trapezoidal instead ofrectangular. The minor base of the trapeze is at the front and as theball rolls and recedes, since the groove is trapezoidal, it widens outand lateral movements become possible, inasmuch as the flexion increasesthis is the rolling" movement. From this basic diagram, the prostheticdevice of this invention consists essentially of a hollow sphere and asolid sphere pivoting in the former, without any other element, whetherbolts or screws. It is only necessary to pivot the two members to eachother, they hold by themselves.

The arrangement may be described as follows 1 the femoral member is thefemale hollow member it has a circular rear aperture having the diameterof the male member. This aperture is such that the male member must bepresented in a perpendicular position with respect to said aperture forengaging same. In other words, it can penetrate only in this right-angleposition. When it has thus penetrated into the female member, it cannotbe removed therefrom, unless said perpendicular relative position isrestored, with a tolerance of a few minutes (max. 3 degrees), whichcannot occur under normal operating or walking conditions since thestretching apparatus locks the parts together. Therefore, any risk ofposterior dislocation is safely precluded.

The male member is the tibial one comprising a shank adapted to be sunkinto the tibia a plate fitting to the tibial surface with a transverseposterior spur bears on said shank. The essential elements of the tibialprosthesis are disposed there over and consist of a relatively bulky,substantially prismatic pivot member having a trapezoidal configurationwith an antero-posterior major side and vertical faces, i.e., a frontface and a rear face, and a top face divided into two segments, namelyan oblique anterior segment inclined downwards and forwards, connectedby an edge to the rear face, for locking the prosthesis in the fullystretched leg position, and a posterior segment carrying the jointmember to be described hereinafter, two non-parallel (trapezoidal)lateral faces constituting the guide walls and locking the assemblylaterally in the stretched position, said two non-parallel facespermitting and limiting in the flexion position a certain degree oflateral movements.

The pivot member proper projects above this irregular parallelipiped byforming firstly a generally hemispherical cap or portion having its baseon the top and connected to a cylindrical segment carrying the otherarticular generally hemispherical cap or portion constituting thespherical joint portion proper. These two generally hemisphericalportions or caps assembled by said cylindrical segment have twodifferent centres, whereby the length of the vertical axis of theassembly is less than the theoretical diameter of the sphere. Thisconstitutes a very important feature of the mechanism to be describedpresently.

The female member comprises likewise a shank adapted to be sunk into thethigh-bone or femur, and carries thereunder the articular member proper.The latter comprises essentially a spherical cavity having the sameradius as the generally hemispherical portions of the male member, saidcavity being therefore greater than the male member pivotally fittedtherein. Hence the possibility of performing lateral and anteroposteriormovements (retroposition in the bent position). Finally, at the bottom,and this constitutes one of the essential features of this prosthesis,the cavity opens into a relatively large trapezoidal recess having ananterior minor base. This recess is of primary importance because it isthe key of the holding device of the prosthetic device it is capital andholds the complete device it replaces all locking and fastening meanshitherto contrived in known prostheses. Therefore, it must be carefullystudied and fitted with precision.

In the backwardand upward direction this curved recess widens out toconstitute a cylindrical recess of which the opening diameter is onlyslightly greater than that of the cylinder of the male member disposedbetween the two generally hemispherical portions; It is through thiscylindrical passage, having its aperture in the vertical plane, that thearticular tibial head or apophyse which is then retained therein, for asexplained in the foregoing, when the angle is or it is possible toremove this apophyse from the femur. Considering the leg movement fromthe fully stretched position and as the knee is bent, there is obtainedon the one hand by virtue of this trapezoidal arrangement and on theother hand by means of the sphero-cylindrical combination of thearticular surfaces, on the other hand, the possibility of accomplishinglateral (rolling) movements and retroposition (pitch) movements. Thissystem affords a movement approaching that of normal physiology, throughan amplitude of 130.

Another advantageous feature characterising the novel prosthesis of thisinvention lies in the fact that it requires but a minimum bonesacrifice. This is due to the specific operating technique which is asfollows in practice, no particular difficulty is experienced The cut isdirected vertically, longitudinally, internally and parallel to theknee-cap, to permit the luxation of the complete extension systemoutwards. The chief points to be adhered to are The surgeon mustcarefully free the lower end of the femur, including the poplitealsurface, a very important factor because it constitutes one of thebearing points of the femoral prosthesis.

The surgeon must then resect all the rear segments of the condyles whichprojects from the plane of said popliteal surface.

He must then attack the bone in the intercondylian notch, so that allthe lateral and anterior portions of the lower end of the femur, notablythe femoral trachlea, are left completely untouched. Similarly, thelower portion of the femoral condyles will be resected as little aspossible(only a few millimeters).

The surgeon will then prepare the axis of the femoral prosthesis aboutwhich he will subsequently dig the recess for the substantiallycylindrical (3 to 4 cm in diameter) femoral membenThis recess extendedat its front portion by the shank channel, is stopped laterally and atthe rear by a plane to be engaged by the prosthesis to be fitted intothe rear portion of the femur by means of a small vertical stud similarto the tibial one.

Upon completion of this sequence, the surgeon will test the femoralprosthesis to ascertain-whether it properly fits in itsrecess or not.

Preparing the tibial end. After the femoral member has been properlyfitted in position, the surgeon may consider'the tibial end. The tibialresection in the vertical direction is more important. A piece about onecentimeter thick, perhaps slightly more, must be removed from the upperend of the tibia the resection depends on the lesions. Sometimes, veryimportant unflateral destructions are observed which make it compulsoryto effect more extensive resections. This resection is performed afterlocating the tibial axis;

Then the surgeon prepares the groove for the pivot by using a drill ofvariable size. At the rear, at a distance of about mm from this groove,he cuts a small channel to be used as an anchoring means.

When the two members have been fitted separately in position, thesurgeontests the assembly. To do this, it is only necessary to place the leg atright angle and to introduce the tibial apophysis into the femoralcavity of the prosthesis.

Thus, the preparation is completed then all the tools are renewed andthe two members are placed in their final positions and sealed withmethyl methacryle cement.

From the foregoing it is clear that this invention can be regarded asconstituting a prosthetic apparatus acting as a substitute for the humanknee, this apparatus being remarkable in that it comprises two elementson the one hand, the upper femoral and female member fitted into thethigh-bone and provided with an articular portion having a convex frontface and defining internally and behind this face a cavity of sphericalcontour opening downwards and backwards, and, on the other hand, a lowermale tibial element formed at. its upper end with an articular portioncomprising two opposite generally hemispherical portions or capsinterconnected by a cylindrical segment, this male articular portionbeing engageable only in the above-defined position at 90 into thefemale femoral element but retained therein in all the other angularposition so as to constitute an'articulation or joint that cannot bedisengaged by itself while permitting the flexion-extension movements aswell as a slight lateral movement as required for the joint plays.

This prosthetic apparatus is characterised in general in that thespherical cavity of the femoral articular portion is open at the rear,this aperture forming a circle of same diameter as that of thecylindrical portion of the male tibial articular portion.

According to a specific feature characterising this prosthetic device,the male articular portion comprises a relatively bulky andsubstantially prismatic pivot element with a trapezoidal base having ananteroposterior side and two vertical faces namely a front face andposterior face, the upper face of this pivot being divided into twosegments namely a front segment extending obliquely downwards andforwards, connected through an edge to the upper face and adapted tolock the device in the fully stretched leg position, and a rear segmentcarrying the articular portion consisting of a pair of oppositegenerally hemispherical caps or portions interconnected by a cylindricalsegment, the two nonparallel trapezoidal lateral faces of this pivotacting as guide means for locking the joint in the stretched-legposition while permitting and limiting in the bent position the lateralmovements of the knee.

According to another feature characterising this prosthetic device thearticular piece proper projects above the pivot having the shape of anirregular parallelipiped, and consists of a first generallyhemispherical cap connected through a cylindrical segment to anotheropposite generally hemispherical cap these two caps having the samecurvature but different centres so that the vertical axis of the malearticular assembly be smaller than the theoretical diameter of thesphere.

According to a further distinguishing feature of this invention, eachmale and female element carries a projecting plate located on this sideof the articulation proper and a rear tongue perpendicular to said plateand adapted to be fitted into the bony portion located behind, in orderto ensure a proper anchorage.

According to a complementary feature of this prosthetic device, each oneof its two main component elements comprises a shank adapted to bedriven into the femoral diaphysis and into the tibial diaphysis,respectively; They are disposed on this side of the male or femalearticular portion and lie on a common axis, so that the prosthesis canbe used for one or the other leg, indifferently. However, they can beinclined slightly, for example by anangle of 5 to 10 (either on thetibial side or on the femoral side), in order to distinguish theright-hand prosthesis from the left-hand one.

The shanks of the two prosthetic elements are engageable into themedullary cavities, respectively, or into cavities specially formed tothis end in the patients femur and tibia.

As already suggested hereinabove, these shanks may advantageously besealed in their corresponding cavities by using an acrylic cement (suchas methyl methacrylate cement).

The walls of the articular members of the prosthetic elements areadvantageously lined with thin layers of a suitable and known lubricantsuch as Teflon, to avoid any seizing.

BRIEF DESCRIPTION OF THE DRAWING:

The diagrammatic drawing attached hereto illustrates a typical form ofembodiment of the novel complete prosthesis of the knee according tothis invention. In the drawing FIG. 1 is a perspective view showing thetwo main elements of this prosthesis, the upper femoral element and thelower tibial element being seen from the rear and separate from eachother to afford a clearer understanding of their relationship FIG. 2 isa similar view of the same elements but in their assembled conditionFIG. 3 is a front elevational view of the two elements in the positionshown in FIG. 2 and FIG. 4 is a fragmentary sectional view showing thebending or flexion movement of the joint, the section being taken alongthe line IVlV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

As illustrated the novel prosthesis of the knee according to thisinvention comprises two elements an upper femoral female elementprovided with an articular portion 11 having a convex front wall 12providing internally of and behind this wall 12 a cavity 13 having aspherical wall open in the downward and backward directions, and a lowertibial male element 14 formed at its upper end with an articular portion15 consisting of a pair of opposite generally hemispherical portions orcaps l6, l7 interconnected by a cylindrical segment 18. This malearticular portion 15 can penetrate into the spherical cavity 13 offemoral element 10 only when the former is presented in a 90-degreeangular position with respect to the latter, but it is retained in thiscavity in all the other permissible positions, so as to constitute anarticulation that cannot be separated while permitting the flexion andstretching movements as well as a slight lateral movement as necessaryfor normal articulation movements.

The spherical cavity 13 formed in the femoral articular portion 11 isopen at the rear and this aperture is of circular configuration as shownat 19 and has the same diameter as that of the cylindrical portion 18 ofthe male tibial articular portion 15. This male portion 15 comprises arelatively bulky and substantially prismatic pivot having a trapezoidalbase 20 with anteroposterior major side and two vertical faces, namely afront face 21 and a rear face 22. The top face of this pivot is dividedinto two segments, i.e., a front segment inclined downwards andforwards, connected to the front face 21 through an edge and adapted tolock the device in the fully stretched position, and a rear segmentcarrying the articular portion comprising the pair of opposite generallyhemispherical portions or caps l6, l7 interconnected by the cylindricalsegment 18. The pair of nonparallel trapezoidal lateral faces of thepivot thus formed act as guide means for locking laterally in thestretched position the patient's leg while permitting and limiting thelateral movements of the knee.

The articular portion 15 projects above the prismatic pivot 20 andcomprises the above-mentioned lower generally hemispherical cap 16connected through a cylindrical segment 18 to the upper generallyspherical hemispherical 17, these two generally hemispherical capshaving the same curvature but different centres, so that the verticalaxis of the male articular assembly thus formed be shorter than thetheorectical diameter of the sphere.

Each element 10 and 14 of this prosthesis of the knee carries aprojecting plate designated by the reference numerals 23 and 24,respectively, each plate being located on this side of the articulationproper, and a rear tongue 25, 26 extending at right angles to said plateand adapted to be fitted into the bony portion located behind, in orderto improve the anchoring action.

The two elements 10, 14 of this prosthesis are provided with shanks 27,28 adapted to be driven into the femoral diaphysis or into the medullarygroove, and into the tibial diaphysis, on this side of the malearticular portion 15 or female articular portion 11, respectively.

These shanks 27, 28 of the prosthesis elements are adapted to be fittedinto medullary cavities or cavities specially formed in the patientsthigh-bone and tibia. Advantageously, the shanks 27, 28 of elements l0,14 are sealed in their cavities by means of an acrylic cement (methylmethacrylate).

The walls of the articular portions of the corresponding elements l0, 14of this prosthesis are advantageously lined with thin layers of asuitable lubricant such as tetrafluorethylene known under the TrademarkTEFLON, to avoid any seizing.

The mode of operation and the specific method of positioning this novelprosthesis in the knee area of the patient has already been explained indetail in the foregoing.

Obviously, the component elements of this prosthesis may be made of anysuitable plastic material or metal or stainless alloy as a function ofthe specific clinical applications and requirements, and it is alsoclear that the various steps of the operation necessary for fitting thisprosthesis, as set forth hereinabove, may be modified without departingfrom the basic principles of the invention, as will be readilyunderstood by those conversant with the art.

What is claimed as new is:

1. A prosthetic device for replacing the articulation of a human knee,which comprises two elements, on the one hand an upper female femoralelement provided with an articular portion having a convex front walladapted to carry the human knee ball and forming internally and behindsaid wall a cavity having a spherical contour opening downwards andbackwards and, on the other hand, a lower male tibial element carryingat its upper end an integral articular portion comprising two oppositegenerally hemispherical portions interconnected by a cylindricalsegment, said cavity and male integral articular portion beingdimensioned so that said male articular portion is releasably engageableinto said female femoral element only when the two elements are disposedat to each other, but remaining locked therein in any other relativeangular position in order to constitute an articulation that cannot bereleased while permitting flexion and extension movements as well as aslight lateral displacement as required for the normal plays of thearticulation.

2. A prosthetic device as set forth in claim 1, wherein said sphericalcavity of the femoral articular portion is open at the rear through acircle having the same diameter as the cylindrical segment of the maletibial articular portion.

3. Prosthetic device as set forth in claim 2, wherein said malearticular portion comprises a relatively bulky pivot of substantiallyprismatic configuration with a trapezoidal base having antero-posteriormajor sides and two vertical faces, namely a front face and a rear face,the upper face of said pivot being divided into two segments, that is, afront segment inclined forwards and downwards, connected through an edgeto the the front face and adapted to lock the device in the fullystretched position, and a rear segment carrying the articular portionconsisting of the pair of opposite generally hemispherical portionsinterconnected by a cylindrical segment, said base having two lateralnonparallel trapezoidal faces, the two lateral non-parallel trapezoidalfaces of said pivot acting as guide means for locking the jointlaterally in the stretched-leg position thereof while permitting andlimiting the lateral movements of the knee in the flexion position.

4. Prosthetic device as set forth in claim 3, wherein said malearticular portion proper projects above said pivot of paralle lipipedicirregular configuration, and consists of a first generally hemisphericalportion or cap, connected through a cylindrical segment to another,opposite generally hemispherical portion or cap, these two generallyhemispherical portions or caps having the same curvature but differentcentres, whereby the vertical axis of the male articular assembly beshorter than the theoretical diameter of the sphere.

5. Prosthetic device as set forth in claim 4, wherein each male andfemale element carries a projecting plate to be located on the side ofthe articulation proper and a rear tongue extending at right angles tosaid plate and adapted to be fitted into the bony portion located behindin order to improve the fastening of the corresponding element.

6. Prosthetic device as set forth in claim 5, wherein each elementcarries an integral shank adapted to be fitted or driven into thefemoral diaphysis or medullary groove and into the tibial diaphysis,said shank being disposed on the same side of the male or femalarticular portion that said plate is located.

7. Prosthetic device as set forth in claim 1, wherein the walls of thearticular portions of said elements are lined with thin layers of asuitable lubricant such as Teflon to prevent the seizing between theinterfitting surfaces.

8068 I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No-3,?95,922 Dated 2 March 1974 Jules Jean-Marie Ernest HERBERT et a1Inventofls) It is certified that error appears in the above-identifiedpatent and that said'Letters Patent are hereby corrected as shown below:

the h line :76] read the first inventor's address for clinque CliniqueSigned and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. A prosthetic device for replacing the articulation of a human knee,which comprises two elements, on the one hand an upper female femoralelement provided with an articular portion having a convex front walladapted to carry the human knee ball and forming internally and behindsaid wall a cavity having a spherical contour opening downwards andbackwards and, on the other hand, a lower male tibial element carryingat its upper end an integral articular portion comprising two oppositegenerally hemispherical portions interconnected by a cylindricalsegment, said cavity and male integral articular portion beingdimensioned so that said male articular portion is releasably engageableinto said female femoral element only when the two elements are disposedat 90* to each other, but remaining locked therein in any other relativeangular position in order to constitute an articulation that cannot bereleased while permitting flexion and extension movements as well as aslight lateral displacement as required for the normal plays of thearticulation.
 2. A prosthetic device as set forth in claim 1, whereinsaid spherical cavity of the femoral articular portion is open at therear through a circle having the same diameter as the cylindricalsegment of the male tibial articular portion.
 3. Prosthetic device asset forth in claim 2, wherein said male articular portion comprises arelatively bulky pivot of substantially prismatic configuration with atrapezoidal base having antero-posterior major sides and two verticalfaces, namely a front face and a rear face, the upper face of said pivotbeing divided into two segments, that is, a front segment inclinedforwards and downwards, connected through an edge to the the front faceand adapted to lock the device in the fully stretched position, and arear segment carrying the articular portion consisting of the pair ofopposite generally hemispherical portions interconnected by acylindrical segment, said base having two lateral non-paralleltrapezoidal faces, the two lateral non-parallel trapezoidal faces ofsaid pivot acting as guide means for locking the joint laterally in thestretched-leg position thereof while permitting and limiting the lateralmovements of the knee in the flexion position.
 4. Prosthetic device asset forth in claim 3, wherein said male articular portion properprojects above said pivot of paralle lipipedic irregular configuration,and consists of a first generally hemispherical portion or cap,connected through a cylindrical segment to another, opposite generallyhemispherical portion or cap, these two generally hemispherical portionsor caps having the same curvature but different centres, whereby thevertical axis of the male articular assembly be shorter than thetheoretical diameter of the sphere.
 5. Prosthetic device as set forth inclaim 4, wherein each male and female element carries a projecting plateto be located on the side of the articulation proper and a rear tongueextending at right angles to said plate and adapted to be fitted intothe bony portion located behind in order to improve the fastening of thecorresponding element.
 6. Prosthetic device as set forth in claim 5,wherein each element carries an integral shank adapted to be fitted ordriven into the femoral diaphysis or medullary groove and into thetibial diaphysis, said shank being disposed on the same side of the maleor femal articular portion that said plate is located.
 7. Prostheticdevice as set forth in claim 1, wherein the walls of the articularportions of said elements are lined with thin layers of a suitablelubricant such as Teflon to prevent the seizing between the interfittingsurfaces.